Physics Help Forum Question about efficiency=MA/IMA

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Mar 25th 2014, 07:08 AM #1 Junior Member   Join Date: Mar 2014 Posts: 2 Question about efficiency=MA/IMA A worker uses a pulley system to raise a 225-N carton 16.5 m. A force of 129 N is exerted and the rope is pulled 33.0 m. a. What is the mechanical advantage of the pulley system. b. What is the efficiency of the system. In the Solution page it said that the MA=fe/fr =225 N/129 N=1.74 and the IMA=de/dr=33.0 m/16.5 m. Can someone tell me what are the MA and IMA stand for？ Thanks.
 Mar 25th 2014, 07:46 AM #2 Senior Member   Join Date: Jun 2010 Location: NC Posts: 366 Of interest, perhaps? Perhaps this is of interest. If not, sorry! http://www.thermospokenhere.com/wp/0...awks_nest.html
Mar 25th 2014, 07:49 AM   #3
Junior Member

Join Date: Mar 2014
Posts: 2
 Originally Posted by THERMO Spoken Here Perhaps this is of interest. If not, sorry! http://www.thermospokenhere.com/wp/0...awks_nest.html
Thank you all the same！ I decide to ask my teacher tomorrow. I still can's understand it.

 Mar 25th 2014, 10:49 AM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,272 MA = "mechanical advantage," and is a measure of force multiplication provided by the lifting mechansim, in this case the pulley system. It is equal to the ratio of the weight of the carton you are lifting to the force you apply on the rope to lift it. So here MA = 225/129 = 1.744, just as you figured it. IMA = "Ideal Mechanical Advantage," and is the mechanical advantage yuo would have under ideal conditions, meaning no losses of power and efficiency = 100%. It's determined by the physical construct of the pulley system, in this case the ratio of the amount of rope you pull to the height the carton is lifted. So IMA = 33/16.5 = 2. Note that the actual MA is less than ideal, so the efficiency of the mechanism is less than 100%. The ratio of MA/IMA gives the efficiency, which is 1.744/2 = 87.2%. Alternatively efficiency can be calculated from the ratio of the work done on the weight being lifted to the amount of work applied done by the person pulling the rope: Eff = (225N x 16.5)/(129N x 33m) = 87.2% Hope this helps.

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